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FreeBSD-SA-20:07.epair                                      Security Advisory
                                                          The FreeBSD Project

Topic:          Incorrect user-controlled pointer use in epair

Category:       core
Module:         kernel
Announced:      2020-03-19
Credits:        Ilja van Sprundel
Affects:        All supported versions of FreeBSD.
Corrected:      2020-02-04 04:29:54 UTC (stable/12, 12.1-STABLE)
                2020-03-19 16:50:36 UTC (releng/12.1, 12.1-RELEASE-p3)
                2020-02-04 04:29:53 UTC (stable/11, 11.3-STABLE)
                2020-03-19 16:50:36 UTC (releng/11.3, 11.3-RELEASE-p7)
CVE Name:       CVE-2020-7452

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:https://security.FreeBSD.org/>.

I.   Background

The epair(4) interface provides a pair of virtual back-to-back connected
Ethernet interfaces.

II.  Problem Description

Incorrect use of a potentially user-controlled pointer in the kernel allowed
vnet jailed users to panic the system and potentially execute aribitrary code
in the kernel.

III. Impact

Users with root level access (or the PRIV_NET_IFCREATE privilege) can panic
the system, or potentially escape the jail or execute arbitrary code with
kernel priviliges.

IV.  Workaround

No workaround is available.  Systems not using epair(4) are not vulnerable.

V.   Solution

Upgrade your vulnerable system to a supported FreeBSD stable or
release / security branch (releng) dated after the correction date,
and reboot.

Perform one of the following:

1) To update your vulnerable system via a binary patch:

Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install
# shutdown -r +10min "Rebooting for a security update"

2) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

[FreeBSD 12.1]
# fetch https://security.FreeBSD.org/patches/SA-20:07/epair.12.patch
# fetch https://security.FreeBSD.org/patches/SA-20:07/epair.12.patch.asc
# gpg --verify epair.12.patch.asc

[FreeBSD 11.3]
# fetch https://security.FreeBSD.org/patches/SA-20:07/epair.11.patch
# fetch https://security.FreeBSD.org/patches/SA-20:07/epair.11.patch.asc
# gpg --verify epair.11.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

VI.  Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path                                                      Revision
- - -------------------------------------------------------------------------
stable/12/                                                        r357490
releng/12.1/                                                      r359141
stable/11/                                                        r357489
releng/11.3/                                                      r359141
- - -------------------------------------------------------------------------

To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:

# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-7452>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-20:07.epair.asc>
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